Fluorescent lamp having partitioned vapor discharge

ABSTRACT

A fluorescent lamp having ultraviolet-producing vapor discharge paths at opposite sides of a partition member and a phosphor coating on at least one side of the member. The partition member is made of ultraviolet-transmitting glass or quartz, so that the phosphor can be excited by ultraviolet radiation from both of the vapor discharge paths.

United States Patent [19] [111 3,928,786

Campbell Dec. 23, 1975 FLUORESCENT LAMP HAVING 3,194,997 7/1965 Waly 313/493 PARTITIONED VAPOR DISCHARGE 3,609,436 9/1971 Campbell 313/204 lnventor: John H.Campbell, Mentor, Ohio General Electric Company, Schenectady, N.Y.

Filed: Oct. 21, 1974 Appl. No.: 516,459

Related US. Application Data Continuation of Ser. No. 375,656, July 2, 1973, abandoned.

Assignee:

US. Cl 313/493; 313/204 Int. Cl. H01J 61/35; H01] 61/42 Field of Search 313/493, 485, 220, 204,

References Cited UNITED STATES PATENTS 6/1938 Barclay 313/190 Primary ExaminerPalmer C. Demeo Attorney, Agent, or FirmNorman C. Fulmer; Lawrence R. Kempton; Frank L. Neuhauser [57] ABSTRACT A fluorescent lamp having ultraviolet-producing vapor discharge paths at opposite sides of a partition member and a phosphor coating on at least one side of the member. The partition member is made of ultraviolettransmitting glass or quartz, so that the phosphor can be excited by ultraviolet radiation from both of the vapor discharge paths.'

5 Claims, 1 Drawing Figure US. Patent Dec. 23, 1975 FLUORESCENT LAMP HAVING PARTITIONED VAPOR DISCHARGE This is a continuation of application Ser'. 375,656, filed July 2, -l973, now abandoned.

BACKGROUND OFTHE INVENTION The invention is in thefleld 'of fluorescent lamps of the type having a phosphor which produces visible light in response to ultraviolet radiation produced by a vapor discharge. I i

Various construction configurations have been devised for fluorescent lamps. U.S. Pat; No. 3,609,436 to John H. Campbell discloses a mercury vapor discharge fluorescent lamp comprising,*in a preferred embodi-' ment, a pair of concentrically positioned tubular glass envelope members-sealed together at their bottom ends and defining a vapor dischargepath concentrically.

SUMMARY OF THE INVENTION Objects of the invention are to provide an improved fluorescent lamp, and to improve the light-producing efficiency of such lamps.

The invention comprises, briefly and in a preferred embodiment, a fluorescent lamp having ultraviolet-producing vapor discharge paths at opposite sides of a partition member, and a phosphor coating at or on at least one side of the member, the partition member being of ultraviolet-transmitting material so that the phosphor can be excited by ultraviolet radiation from both vapor discharge paths. In a preferred embodiment, the lamp comprises a pair of concentrically positioned glass tubes sealed together at their bottom ends and defining a vapor discharge region concentrically folded back upon itself between the bottom end of the inner tube and the bottom end of the lamp between the concentric tubes, the inner tube being made of ultraviolet-transmitting material and the outer tube being made of ultraviolet-absorbing material. Three phos phor coatings may be provided: on the inner and outer surfaces of the inner tube and on the inner surface of the outer tube. Alternatively, two phosphor coatings are provided: on the outer surface of the inner tube and on the inner surface of the outer tube.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of the drawing is a perspective view, partly broken away, of a preferred embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT The lamp shown comprises a tubular glass outer envelope member 11 having a closed upper end 12 and hermetically sealed at the bottom end thereof to a glass header 13. A tubular glass inner envelope member 14 is 2 concentrically arranged within the outer member 11 and is sealed at the bottom end thereof to the header 13. Support wires 15 aid in positioning the envelope members. The upper end of the inner tube 14 is open, and is spaced from the closed upper end 12 of the outer tube 11 so as to provide a vapor discharge pathfrom the inner envelope member 14 to the space between it and'the outer envelope member 11. A common electrode 16, shown as being a filament type of cathode, is positioned within and near the bottom end of the inner envelope tube 14 and is supported by a pair of lead-in wires which extend out of the lamp through the header 13. A plurality of additional cathode electrodes 17a, 17b, etc., are arranged equally apart in a circular configuration near the bottom of the lamp in the space between the inner envelope member 14 and the outer envelope member 11, and are individually supported by lead-in wires extending downwardly through the header 13 to the outside of the lamp. Phosphor coatings 21, 22, and 23 are respectively provided on the inner surface of the inner envelope member 14, on the outer surface thereof, and on the inner surface of the outer envelope member 11. A small amount of mercury is included in the lamp, along with an inert gas such as argon, as is customary in fluorescent lamps. Further details of the general lamp construction are disclosed in the above-referenced U.S. Pat..No.. 3,609,436. The tubular members 11 and 14 need not be cylindrical.

In operation, switching circuitry is connected to electrodes l6 and 17 and functions to sequentially activate the various electrodes 17 in turn so that a mercury vapor discharge, which emits ultraviolet light, extends from the common electrode 16 upwardly through the inner envelope member 14 and then downwardly through the space between the inner and outer envelope members 14 and 11 in a manner which jumps from one to the next of the electrodes 17 so that the discharge rotates rapidly around the inner envelope member 14 and within the outer envelope member 11. Suitable switching circuitry and details of operation are disclosed in the above-referenced patent.

In accordance with the invention, the inner tube 14 is made of ultraviolet-transmitting glass or quartz, and the outer tube 11 may be made of ultraviolet-absorbing glass such as is normally used for fluorescent lamps. Thus, each of the phosphor layers 21, 22, and 23 receives ultraviolet excitation from'the portion of the vapor discharge within the inner tube 14 and also from the portion of the discharge that is between the two tubes. More specifically, some of the ultraviolet energy produced by the discharge within the inner tube 14 strikes and excites the inner phosphor coating 21, and some of this ultraviolet energy passes through the wall of the inner tube 14 and strikes and excites the phosphor coating 22 and also probably the third phosphor coating 23. Similarly, the ultraviolet energy produced in the discharge between the two tubes 11 and 14 strikes and excites all three of the phosphor coatings. The result is greater brightness and improved efficiency. Such a lamp produced 30% more lumen output than a similar lamp with an inner tube 14 of conventional ultraviolet-absorbing glass.

The innermost phosphor coating 21 can be eliminated without substantially adversely affecting the amount of light output. This is because relatively more ultraviolet energy from within the inner tube 14 will pass through the tube wall (unimpeded by the phosphor 21) and excite the phosphor 22. Elimination of 3 the phosphor layer 21 has an advantage of reduced manufacturing cost. The different phosphor layers can be of different phosphor compositions which have different color-rendering characteristics, the total color characteristic of light from the lamp being a combination of that produced by the different phosphor layers. The innermost phosphor layers 22, and 21 if provided, should be rather thin so as to increase the transmission of ultraviolet therethrough.

While preferred embodiments of the invention have been shown and described, various other embodiments and modifications thereof will become apparent to persons skilled in the art, and will fall within the scope of the invention as defined in the following claims. Terminology herein concerning the vapor discharge paths and phosphor coatings being at opposite sides of a partition member is not necessarily limited to their being directly on or adjacent to the partition member, but also includes the phosphor coating 23 which is spaced from one side of the partition member 14.

What l claim as new and desire to secure by Letters Patent of the United States is:

l. A fluorescent lamp comprising a partition member, means providing ultraviolet-producing vapor discharge paths at opposite sides of said partition member, and phosphor at only one side of said partition member, said partition member being of ultraviolet-transmitting material so that said phosphor can be excited by ultraviolet radiation from both of said vapor discharge paths.

2. A lamp as claimed in claim 1 including a tubular member, said partition member comprising the wall of said tubular member, said vapor discharge paths extending axially along opposite sides of said wall of the tubular member, and said phosphor comprising a phosphor layer on only the outside surface of said tubular member.

3. A lamp as claimed in claim 1 including inner and outer tubular members positioned coaxially with respect to each other, means interconnecting said tubular members at the bottom ends thereof, the upper end of said outer tubular member being closed and spaced above the upper end of said inner tubular member, first electrode means near the bottom end of said inner tubular member and second electrode means between said tubular members near the bottom ends thereof, said vapor discharge paths extending in series between said first and second electrode means, said partition member comprising said inner tubular member and having a phosphor layer only on its outer surface.

4. A lamp as claimed in claim 3 in which said outer tubular member is of ultraviolet-absorbing material.

5. A lamp as claimed in claim 3 including a phosphor layer on the inner surface of said outer tubular mem- 

1. A fluorescent lamp comprising a partition member, means providing ultraviolet-producing vapor discharge paths at opposite sides of said partition member, and phosphor at only one side of said partition member, said partition member being of ultraviolet-transmitting material so that said phosphor can be excited by ultraviolet radiation from both of said vapor discharge paths.
 2. A lamp as claimed in claim 1 including a tubular member, said partition member comprising the wall of said tubular member, said vapor discharge paths extending axially along opposite sides of said wall of the tubular member, and said phosphor comprising a phosphor layer on only the outside surface of said tubular member.
 3. A lamp as claimed in claim 1 including inner and outer tubular members positioned coaxially with respect to each other, means interconnecting said tubular members at the bottom ends thereof, the upper end of said outer tubular member being closed and spaced above the upper end of said inner tubular member, first electrode means near the bottom end of said inner tubular member and second electrode means between said tubular members near the bottom ends thereof, said vapor discharge paths extending in series between said first and second electrode means, said partition member comprising said inner tubular member and having a phosphor layer only on its outer surface.
 4. A lamp as claimed in claim 3 in which said outer tubular member is of ultraviolet-absorbing material.
 5. A lamp as claimed in claim 3 including a phosphor layer on the inner surface of said outer tubular member. 